We are requesting funds to purchase a Coulter EPICS elite flow cytofluorimeter for our facility. The flow cytofluorimeter facility at Wistar was established over 9 years ago and it is staffed by two experienced technicians. Many investigators at Wistar and in other institutions are routinely using the facility and their scientific work heavily depends on it. We have presently a Becton Dickinson FACS IV and an Ortho Diagnostic Instruments Cytofluorograf 50HH. However, both these instruments are over 8 years old and, in the case of the Cytofluorograf 50HH, because Ortho Diagnostic Instruments is no longer in business, technical breakdowns are becoming increasingly frequent, maintenance is difficult. Also, flow cytofluorimetry technology has rapidly progressed and several techniques required by the scientific projects of Wistar investigators can not be performed with the available instruments. Acquisition of the EPICS Elite instrument will allow us to maintain an efficient flow cytofluorimetry facility and will add ability to sort cells with significantly higher purity and velocity, ability to perform 3 and 4 color immunofluorescence analysis, efficient use of dyes requiring U.V. activation (e.g. Indo-1 and Hoechst 33342), and simultaneous analysis of cell cycle by DNA staining and surface antigens by 2 color immunofluorescence. Acquisition of an additional instrument will allow us to meet the increasing demand on the available instrumentation. We propose to use EPICS Elite for a variety of projects, including cellular immunology, differentiation, control of cell growth, and tumor biology.